1. Field
The present invention relates generally to data communication, and more particularly to techniques for using a decision feedback equalizer and a linear equalizer in a manner to provide improved performance at a receiver.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users and may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), or some other multiple access techniques. These systems may also be wireless Local Area Network (LAN) communication systems, such as those that conform to the IEEE standard 802.11b.
For a wireless communication system, data is processed at a transmitter and sent to a receiver via a wireless communication channel. This channel may experience frequency selective fading, which is characterized by different amounts of signal attenuation across the system bandwidth. The frequency selective fading causes Inter-Symbol Interference (ISI), which is a phenomenon whereby each symbol in a received signal acts as distortion to subsequent symbols in the received signal. The ISI distortion degrades performance by impacting the ability to correctly detect the received symbols.
An equalizer may be used to mitigate the deleterious effects of ISI. A Linear Equalizer (LE) and a Decision Feedback Equalizer (DFE) are two equalizer structures that may be used to equalize a received signal. The DFE uses a feedback filter to derive an estimate of the ISI distortion based on prior detected symbols. The DFE can effectively remove the ISI distortion if the detected symbols are reliable. Otherwise, errors in the detected symbols propagate to the distortion estimate and degrade performance. The LE performs equalization without the use of a feedback filter. In general, the DFE and LE are better suited for use under different operating conditions.
There is therefore a need in the art for techniques to select either the DFE or LE for use to equalize a received signal, and to efficiently adapt the selected equalizer.